Various positive displacement rotary pumps have heretofore been provided for circulating various viscosity products; however, such pumps have been ineffective in handling such products at pressures within the range of 200-350 psi. When operating within such a pressure range, such pumps have been beset with one or more of the following shortcomings: (a) serious shaft deflection occurs; (b) an inordinate amount of bearing wear results; (c) serious galling between the rotors and the cavity surfaces; (d) the rotors are higly susceptible to product corrosion and product abrasiveness; (e) the shafts are not effectively isolated from the product thereby causing the potential for serious contamination problems; and (f) makes disassembly of the pump for cleaning and maintenance a difficult and time-consuming operation.